From WO 99/50165, for example, a so-called overload control is known, wherein the elevator load is sensed by means of a load sensor. If the elevator load exceeds a base limit-value, a travel operation is made impossible by the elevator doors being prevented from closing. Simultaneously, an acoustic signal is issued which draws attention to the overload. Only when the load sensor senses that the elevator load no longer exceeds the base limit-value, do the doors close, and is the travel operation started, whereupon the overload signal is deactivated.
This ensures that the specified limit-values for safe operation of the elevator in relation to loading of the suspension means, driving power and braking power of the drive, braking force and holding force of the brake device, and suchlike, are not exceeded. Also, for reasons of safety, these limit-values are generally selected relatively low when they are defined, by the theoretical values that would be possible mechanically, and for the drive, being divided by safety factors greater than 1 before they are compared with the maximum loads that occur in normal operation.
Also known, for example from the said WO 99/50165, is the use of elevators also for the evacuation of persons, for example in the case of fire or bomb-threat. Above a certain height of building, such an evacuation, particularly of older people, and/or those with disabilities, can take place faster than via conventional escape routes, such as stairways. In fact, in extremely tall buildings, elevators are virtually the only possible means of evacuating the building sufficiently rapidly.
Particularly in such situations, in which the risk of failure of the elevator due to overloading recedes into the background by comparison with the consequences of insufficiently timely evacuation of persons, the deliberate selection for safety reasons of low limit-values based on normal operation prevents utilization of the full technically possible transportation capacity of the elevator. There are similarities also in other situations, for example briefly occurring peak-traffic situations, in which the low limit-values that are appropriate for normal operation unnecessarily restrict the elevator capacity.